U2141

Code

OPEL U — Network/User

CAN-Bus No Communication with REC (Rear Electrical Centre)

Brand: OPEL

Type: U — Network/User

Views: UK: 7 EN: 6 RU: 5

AI status

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ready

Completed 100%

Page language: EN

Rear electrical functions inoperative or intermittent (tail lights, wipers, rear locking, sensors)
Multiple related fault codes stored from other modules
Instrument cluster warning message: 'Service CAN' or module not present
Impossible to communicate with REC via diagnostic tool
Possible battery drain or parasitic current if shorted

Read and record all stored DTCs and freeze frame data from all modules
Check battery voltage and charging system health
Inspect fuses and relays supplying the REC; verify presence of fuse voltage
Visually inspect REC connectors and rear harness for damage or corrosion
Scan network to see if REC module appears on LIN/CAN list
Measure CAN bus termination resistance (approx. 60 ohms across CAN_H and CAN_L) with ignition off

Idle voltage (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (half battery)
Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (approx. ±1 V from idle)
Termination resistance: ~60 Ω measured between CAN_H and CAN_L (two 120 Ω in parallel)
Typical CAN bit rates: 500 kbps or 250 kbps depending on vehicle network; verify vehicle spec
Low-voltage or noisy signals, missing frames, or constant dominant state indicate wiring/module fault

Capture the current DTCs from all modules, note occurrence count and freeze frame data.
Verify battery voltage (12.4–12.8 V at rest) and system ground connections; charge if low.
Check fuses/relays feeding the REC; restore power to REC and confirm module wakes on the network.
Visually inspect REC connector and rear harness for corrosion, bent pins, or water ingress; repair as needed.
With ignition on, use a scan tool: attempt to communicate with REC. If no response, proceed to wiring checks.
Measure resistance between CAN_H and CAN_L at the REC connector with ignition off (~60 Ω).
Probe CAN_H and CAN_L with an oscilloscope while crank/drive or exercising network to observe normal differential waveform and bit activity; look for constant dominant or missing frames.
If abnormal waveform or short detected, disconnect downstream modules one at a time (or isolate harness sections) to locate short or faulty node.
Check for CAN lines shorted to ground or battery by measuring voltage to ground on each line (recessive ≈ 2.5 V).
If wiring and power are good, suspect REC module failure; confirm by substituting a known-good REC or bench-testing module if available.
Repair or replace damaged wiring/connectors or replace module as indicated. Clear codes and road test to verify repair.
After repair, re-scan all modules and confirm no related codes return.

⚠️ Status

No communication with Rear Electrical Centre (REC) on CAN bus. REC module not responding to network requests.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours

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